Avraham and Yaakov wanted to do chesed for Hashem, so they said "Wipe them out in order to sanctify your name!" But Yitzchak was בטל ומבוטל. Ashes on the mizbeach. He was moser nefesh for to die for Hashem. So he can now defend the Jews [not for his own sake because he was nullified] and be moser nefesh to save them. Like he said [in the gemara]: הא קריבית נפשי קדמך - I sacrificed myself before you. It is not about me at all. [Maybe if Avraham or Yaakov had asked to save the Jews it might have seemed that they had a personal stake in the matter. But with Yitzchak there was no such concern].
See what Rav Moshe Schwalb, the Mashgiach in Gatehead wrote:
